Rheological cure curve

This paper describes the general methodology and some results of the study of thermoset systems by rheological techniques, chiefly in steady rotation. Analysis of the experimental cure curve is described in detail, and the use of chemorheologioal data to correlate and predict product performance as well as provide guidance for formulation, is discussed. 

Tile models proposed for the description of the complete rheological curves are also based on a mathematical approximation (4). The power equations are characterized by their similarity to the second group of models which were used to describe the incomplete rheological cures and include the ... 

Typical rheological curves obtained during a diepoxy-diamine reaction are shown in Fig. 6.3. The cure temperature (T = 90°C) is well above the glass transition temperature of the fully cured network (Tgoo 35°C), which means that only gelation occurs. Three typical regions are observed during cure (Matejka, 1991). 

In spite of the fact that the rheological behavior during c ire of the Ashlemd polyester resin looks very similar to that of the Dow vinyl ester resin, the Ashlcuid polyester resin is found to be more reactive them the Dow vinyl ester resin, with the same formulation emd initiator system used in this study. Some iii Kjrtemt differences in the rheological responses are reflected on (1) the values of (2) the time at which shrinkage begins to occur when the fluid is at rest emd (3) the slope of the -( ii- 22 versus cure time curve. 

Figure 5-7 shows the frequency dependences of the storage and loss moduli at various times during the reaction, from 6 minutes before G to 6 minutes after it. Note that at tc (labeled Gel Point in Fig. 5-7), G and G" follow power laws over the entire frequency range For times less than this (labeled —2 and —6 in Fig. 5-7), the curves slope downward at low frequencies, which is indicative of fluid-like behavior, while at times after the gel point (labeled -t-2 and - -6), G flattens at low frequency—a characteristic of solidlike behavior. Thus, the intermediate state with a power-law frequency dependence over the whole frequency range is the transitional state between liquid-like and solid-like behavior, and therefore it defines the gel point. This rheologically determined gel point coincides with the conventional value, namely the maximum degree of cure at which...

Figure 10.2 Rheological changes in epoxy-amine resin during cure (a) TG (b) Transitions as defined by e" curves Source Author s own files)...

The profiles of gelation curves determined for amine-cured epoxy resins correspond to the variation of CL intensity on time and the narrow differences between the times of gelation obtained from chemiluminescence experiments and rheological analysis were reported (Fig. 53)[95K1]. 

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